This application claims the priority of German Patent Application, Serial No. 101 43 290.9, filed Sep. 4, 2001, pursuant to 35 U.S.C. 119(a)-(d), the subject matter of which is incorporated herein by reference.
The present invention relates, in general, to an arcuate double-layer pipe for a pipeline for fluidic transport of abrasive solids, such as concrete.
U.S. Pat. No. 5,275,440 describes a double-layer pipe bend which includes an inner pipe portion of cast steel, an outer pipe portion made of weldable steel and surrounding the inner pipe, and connecting flanges at the ends of the pipe bend.
Apart from problems arising during use and achieving of a long service life, fabrication and assembly of an arcuate double-layer pipe poses great challenges to the manufacturer. Although the fabrication of an arcuate pipe portion of highly wear-resistant material can fairly easily be realized, the integration of such a pipe portion in pipe bends of weldable steel for producing operational arcuate double-layer pipes still poses a problem because the inner pipe portion of highly wear-resistant material represents a delicate component and cannot be welded. Moreover, manufacturing-based tolerances of such inner pipe portions must be taken into account.
It would therefore be desirable and advantageous to provide an improved arcuate double-layer pipe for a pipeline for fluidic transport of abrasive solids, which obviates prior art shortcomings and which is simple in structure and can easily and economically be installed while still being reliable in operation.
According to one aspect of the present invention, an arcuate double-layer pipe for a pipeline for fluidic transport of abrasive solids, includes an inner pipe portion made of wear-resistant material; an outer pipe portion of weldable steel in surrounding relationship to the inner pipe portion; and a pair of coupling collars made of weldable steel and placed on opposite ends of the inner pipe portion, with each coupling collar having a ring-shaped insert of wear-resistant material and a rim-like projection so that the inner pipe portion extends between the ring-shaped insert of one coupling collar and the ring-shaped insert of the other coupling collar and is overlapped on the opposite ends by the rim-like projections of the coupling collars, wherein the rim-like projections of the coupling collars engage interiorly into opposite ends of the outer pipe portion for centering the outer pipe portion, with the opposite ends of the outer pipe portion being welded to the coupling collars.
The present invention resolves prior art problems by providing the coupling collars with rim-like projections which are constructed on the inside such that the ends of the inner pipe portion can be reliably received. The end faces of the inner pipe portion are then arranged in confronting disposition with respect to the ring-shaped inserts in the coupling collars. The projections are able to engage into the ends of the outer pipe portion for centering purposes to thereby comply reliably with the manufacturing-based tolerances of the inner pipe portion. Except for the welded joints between the coupling collars and the ends of the outer pipe portion, the assembly of the double-layer pipe involves only pure jointing and latching connections.
According to another feature of the present invention, the projections may also have a conical outer circumference. In this way, assembly of the outer pipe portion with the projections of the coupling collars is facilitated. Of course, it is also conceivable to conform the comparably thin outer pipe portion to the cylindrical projections through application of a respective shaping process, e.g. pressing.
According to another feature of the present invention, each of the coupling collars is provided in the area of the projection with a radially inwardly directed stop surface. This further facilitates the assembly of a double-layer pipe. The stop surfaces may be constructed as a continuous surface or in the form of spaced-apart lugs.
According to another feature of the present invention, each of the coupling collars has an inner pipe portion distal end face and may be provided at the inner pipe portion distal end face with a radially inwardly directed restraining surface. The provision of the stop surface and the restraining surface enables to carry out the welding operations for connecting the outer pipe portion to the coupling collars, and subsequently to join the ring-shaped inserts in the coupling collars. In this way, wearing properties, in particular of hardened inserts, are not adversely affected. The restraining surface may be designed during fabrication of the coupling collars as axial projection, either as continuous member extending about the circumference or formed as individual tabs in spaced-apart circumferential disposition. Once the inserts are joined in the coupling collars and abut against the respective stop surfaces, it is only necessary to bend the restraining tabs inwardly against the inserts to correctly position the inserts. Of course, it is also possible, to place the inserts first in the coupling collars and then weld the projections to the outer pipe portion.
According to another feature of the present invention, the end face of each of the coupling collars may be grooved between the restraining tabs and an outer surface of the coupling collar. The provision of the groove facilitates a bending of the tabs, especially when the restraining surface is continuous.
According to another feature of the present invention, the outer pipe portion may have a wall which is traversed by at least one opening, e.g. a bore. In this way, a supporting material may be introduced through the opening into the gap between the outer pipe portion and the inner pipe portion to better prop up the inner pipe portion which is sensitive to impact and shock.
The coupling collars may be provided with radially projecting flanges formed with bores for receiving bolts. The coupling collars may, however, also be provided with circumferential coupling grooves, especially of trapezoidal cross section for engagement of cup-shaped coupling members.